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lower valley, 200 leagues long, which forms the country of Egypt. This valley, though of such immense length, is only from one to six leagues in breadth, and bounded on either side by the rocky mountains of the desert. Its habitable and cultivated portion is entirely confined to that part of the surface which is overflowed by the inundations of the Nile : as far as the waters rise, the soil is of extraordinary fertility; beyond it the blowing desert is alone to be seen. At the distance of 50 leagues from the sea, the Nile divides itself into two branches, which fall into the Mediterranean, one at Rosetta, the other at Damietta. The triangle having these two branches for its sides, and the sea for its base, is called the Delta, and constitutes the richest and most fertile district of Egypt, being perfectly level, intersected by canals, and covered with the most luxuriant vegetation.

The soil of this singular valley was originally as barren as the arid ridges which adjoin it; but it has acquired an extraordinary degree of richness from the well-known inundations of the Nile. These floods, arising from the heavy rains of July and August, in the mountains of Abyssinia, cause the river to rise gradually, during a period of nearly three months. It begins to swell in the middle of June, and continues to rise till the end of September, when it assumes the height of 16 or 18 feet. The fertility of the country is just in proportion to the height of the inundation; hence it is watched with the utmost anxiety by the inhabitants, and public rejoicings are ordered when the Nilometer at Cairo indicates a foot or two of greater depth of water than usual. It never rains in Egypt. Centuries may elapse without more than a shower or drizzling mist moistening the surface of the soil. Hence cultivation can only be extended beyond the level to which the water rises by an artificial system of irrigation ; and the efforts made in this respect by the ancient inhabitants constitute, perhaps, the most wonderful of the many monuments of industry which they have left to succeeding ages.

During the inundation, the level plain of Egypt is flooded with water; the villages, detached from each other, communicate only by boats, and appear, like the islands on the laguna of Venice, in the midst of the watery waste. No sooner, however, have the floods retired, than the soil, covered to a considerable depth by a rich slime, is cultivated and sown, and the seed, vegetating quickly in that rich mould, and under a tropical sun, springs up, and in three months yields a hundred, and sometimes a hundred-and-fifty-fold. During the whole winter months, the soil is covered with the richest harvests, besprinkled with flowers, and dotted by innumerable flocks; but in March the great heats begin, the earth cracks from excessive drought, vegetation disappears, and the country is fast relapsing into the sterility of the desert, when the annual floods of the Nile again cover it with their vivifying waters.

All the varied productions of the temperate and the torrid zones flourish in this favoured re

gion. Besides all the grains of Europe, Egypt produces the finest crops of rice, maize, indigo, cotton, and senna. It has no oil, but the opposite coasts of Greece furnish it in abundance ; nor coffee, but it is supplied from the adjoining mountains of Arabia. Hardly any trees are to be seen over its vast extent; a few palms and sycamores in the villages, alone, rise above the luxuriant vegetation of the plain. Its horses are celebrated over all the world for their beauty, their spirit, and their incomparable docility; and it possesses the camel, that wonderful animal, which can support thirst for days together, tread without fatigue the moving sands, and traverse, like a living ship, the ocean of the desert. Every year immense caravans arrive at Cairo from Syria and Arabia on the one side, and the interior of Africa on the other. They bring all that belongs to the regions of the sun-gold, ivory, ostrich-feathers, gum, aromatics of all kinds, coffee, tobacco, spices, perfumes, with the numerous slaves, which mark the degradation of the human species in those favoured countries. Cairo becomes, at that period, an entrepôt for the finest productions of the earth, for those which the genius of the West will never be able to rival, but for which its opulence and luxury afford a never-failing demand. Thus the commerce of Egypt is the only one on the globe which never can decay; but must, under a tolerable government, continue to flourish, as long as the warmth of Asia furnishes articles, which the industry and perseverance of Europe are desirous of possessing

In ancient times, Egypt and Lybia, it is well known, were the granary of Rome; and the masters of the world depended for their subsistence on the floods of the Nile. Even at the time of the conquests of the Mahometans, Egypt is said to have contained 20,000,000 of souls, including those who dwelt in the adjoining oasis of the desert. This vast population is by no means incredible, if the prodigious fertility of the soil, where water can be conveyed, is considered ; and the extent to which, under a paternal government, the system of artificial irrigation can be carried. It is to the general decay of all the great establishments for the watering of the country, which the industry of antiquity had constructed, that we should ascribe the present limited extent of agriculture, and the perpetual encroachments which the sands of the desert are making on the region of human cultivation.

A.

LESSON III.

THE DIVING-BELL.

Compressible ingenious stationary condensed contrivance replaced truncated cavities

velocity parallel orifice

accident prominences communication apprehension immediately quantity

prevented To illustrate the principle of this machine, take a glass tumbler; plunge it into water, with the mouth

downwards; you will find that very little water will rise into the tumbler; which will be evident, if you lay a piece of cork upon the surface of the water, and put the tumbler over it; for you will see, that though the cork should be carried far below the surface of the water, yet that its upper side is not wetted, the air which was in the tumbler having prevented the entrance of the water; but as air is compressible, it could not entirely exclude the water, which, by its pressure, condensed the air a little.

The first diving-bell of any note was made by Dr. Halley. It is most commonly made in the form of a truncated cone, the smaller end being closed, and the larger one open. It is weighted with lead, and so suspended, that it may sink full of air, with its open base downwards, and as near as may be, parallel to the horizon, so as to close with the surface of the water. Mr. Smeaton's diving-bell was a square chest of cast-iron, four feet and a half in height, four feet and a half in length, and three feet wide, and afforded room for two men to work in it. It was supplied with fresh air by a forcing pump. The sinking and raising of the diving-bell, invented by Dr. Halley, depending entirely on the people at the surface of the water, and being besides of considerable weight, so as to occasion much labour, with a risk of the breaking of the rope, by which it was to be raised, to the sure destruction of those within ; a divingbell has been invented by Mr. Spalding, of Edinburgh, to remedy these defects, and prevent the

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